Analysis of cDNA libraries prepared from EIAV-infected cells revealed multiple species of cDNAs that could encode tat, rev and novel forms of env products. Two new polycistronic mRNAs were identified that can encode, tri- and bi-exonic rev species as well as transmembrane proteins with distinct amino terminal sequences. Rev products were detected in infected cells and, surprisingly, in virions. We previously reported the isolation of a replication competent but non-pathogenic EIAV molecular clone. In attempts to generate a pathogenic clone, sequences representing the entire EIAV genome were isolated by the PCR technique from diseased animals. These were compared to those of a full-length infectious but non-pathogenic clone (Cl22) and were found to be well- conserved except in the env region. Initial studies indicate that the major differences in env sequences do not account for the marked difference in cell tropism between tissue culture-adapted (i.e., Cl22) and wild type virus isolates. Studies on the pathogenic properties of the chimeras is in progress. Integrated and unintegrated forms of the caprine arthritis-encephalitis (CAEV) genome in infected cells were cloned and characterized. The majority of each species contained deletions that removed varying extents of pol, env and 3' LTR sequences but not gag. Evidence was obtained that the deleted forms were transcriptionally active and could generate deleted virion mRNAs. The influence of these defective virions on CAEV infections is being determined. The sequence of the genome of the lymphoproliferative disease virus (LPDV) of turkeys was determined. Although acutely oncogenic, LPDV does not contain an oncogene. Sequence comparisons revealed that LPDV represents a unique class of avian type C oncovirus most closely related to chicken leukosis viruses.